Fluoroelastomers are well known in the art; see for example U.S. Pat. Nos. 4,214,060; 4,281,092; 5,789,489; 6,512,063 and 6,924,344 B2. They may be partially fluorinated (i.e. contain copolymerized units of at least one monomer having C—H bonds such as vinylidene fluoride, ethylene or propylene) or be perfluorinated (i.e. contain copolymerized units of monomers not having C—H bonds). Examples of fluoroelastomers include, but are not limited to copolymers of i) vinylidene fluoride, hexafluoropropylene and, optionally, tetrafluoroethylene; ii) vinylidene fluoride, perfluoro(methyl vinyl ether) and, optionally, tetrafluoroethylene; iii) tetrafluoroethylene and propylene; and iv) tetrafluoroethylene and perfluoro(methyl vinyl ether). Optionally, the fluoroelastomer may further comprise copolymerized units of a cure site monomer to assist in the crosslinking of the elastomer.
Shaped fluoroelastomer articles (e.g. seals, gaskets, tubing, etc.) are typically made by first compounding the fluoroelastomer with other ingredients such as filler, curative, process aids, colorants, etc., shaping the compound (e.g. by extrusion though a die or by molding) and then curing the shaped article.
Non-fibrillating fluoroplastic particles are often employed as fillers in fluoroelastomers. However, high loading of non-fibrillating fluoroplastics is required in order to achieve a modulus or hardness suitable for some end uses. High loading can cause the compression set resistance to undesirably increase.
Fibrillatable fluoroplastic fillers for fluoroelastomers have been disclosed previously, e.g. U.S. Pat. No. 4,520,170. However, the compositions are made by a cumbersome cryogenic pulverization process. It would be desirable to have a more commercially feasible process for introducing fibrillating fluoroplastic filler into a fluoroelastomer composition.